Buggy code:
public class GameClient { public static void main ( String [ ] args ) throws RemoteException { if ( ( args . length ) < 2 ) { System . err . println ( "Usage:\njava<seq2seq4repair_space>GameClient<seq2seq4repair_space><host><seq2seq4repair_space><port>" ) ; return ; } String hostname = args [ 0 ] ; int registryport = Integer . parseInt ( args [ 1 ] ) ; System . setProperty ( "java.security.policy" , "mud.policy" ) ; System . setSecurityManager ( new RMISecurityManager ( ) ) ; try { String regURL = ( ( ( "rmi:////" + hostname ) + ":" ) + registryport ) + "//GameServer" ; MUD gameService = ( ( MUD ) ( Naming . lookup ( regURL ) ) ) ; System . out . println ( "Welcome<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>MUD.<seq2seq4repair_space>What<seq2seq4repair_space>is<seq2seq4repair_space>your<seq2seq4repair_space>name?" ) ; BufferedReader in = new BufferedReader ( new InputStreamReader ( System . in ) ) ; Player player = null ; boolean registered = false ; while ( registered == false ) { String username = in . readLine ( ) . trim ( ) ; if ( gameService . isValidPlayerName ( username ) ) { if ( gameService . isUniquePlayerName ( username ) ) { System . out . print ( ( ( "Do<seq2seq4repair_space>you<seq2seq4repair_space>want<seq2seq4repair_space>to<seq2seq4repair_space>play<seq2seq4repair_space>as<seq2seq4repair_space>" + username ) + "?<seq2seq4repair_space>(yes//no)<seq2seq4repair_space>" ) ) ; String confirmation = in . readLine ( ) . trim ( ) ; Pattern positivePattern = Pattern . compile ( "^y(es){0,1}$" , Pattern . CASE_INSENSITIVE ) ; Pattern negativePattern = Pattern . compile ( "^n(o){0,1}$" , Pattern . CASE_INSENSITIVE ) ; Matcher positiveMatcher = positivePattern . matcher ( confirmation ) ; Matcher negativeMatcher = negativePattern . matcher ( confirmation ) ; if ( ( confirmation . equals ( "" ) ) || ( positiveMatcher . matches ( ) ) ) { player = new Player ( username , 100.0 ) ; player . currentLocation = gameService . getStartingLocation ( ) ; if ( ! ( gameService . join ( player ) ) ) { System . out . println ( "There<seq2seq4repair_space>was<seq2seq4repair_space>a<seq2seq4repair_space>problem<seq2seq4repair_space>signing<seq2seq4repair_space>you<seq2seq4repair_space>up.<seq2seq4repair_space>Please<seq2seq4repair_space>try<seq2seq4repair_space>again." ) ; } else { registered = true ; } } else if ( negativeMatcher . matches ( ) ) { System . out . print ( "What<seq2seq4repair_space>is<seq2seq4repair_space>your<seq2seq4repair_space>name?<seq2seq4repair_space>" ) ; } } else { System . out . println ( "This<seq2seq4repair_space>name<seq2seq4repair_space>is<seq2seq4repair_space>already<seq2seq4repair_space>taken.<seq2seq4repair_space>Please<seq2seq4repair_space>choose<seq2seq4repair_space>a<seq2seq4repair_space>different<seq2seq4repair_space>one." ) ; } } else { System . out . println ( "This<seq2seq4repair_space>is<seq2seq4repair_space>not<seq2seq4repair_space>a<seq2seq4repair_space>valid<seq2seq4repair_space>username.<seq2seq4repair_space>Please<seq2seq4repair_space>choose<seq2seq4repair_space>a<seq2seq4repair_space>different<seq2seq4repair_space>one." ) ; } } System . out . println ( ( ( "Welcome,<seq2seq4repair_space>" + ( player . name ) ) + ".<seq2seq4repair_space>Type<seq2seq4repair_space>a<seq2seq4repair_space>command<seq2seq4repair_space>to<seq2seq4repair_space>start." ) ) ; System . out . println ( "Type<seq2seq4repair_space>'help'<seq2seq4repair_space>or<seq2seq4repair_space>?'<seq2seq4repair_space>if<seq2seq4repair_space>you<seq2seq4repair_space>need<seq2seq4repair_space>help." ) ; String command = "" ; while ( ( ! ( command . equals ( "quit" ) ) ) && ( ! ( command . equals ( "exit" ) ) ) ) { <START_BUG> Pattern goCommandFormat = Pattern . compile ( "^go<seq2seq4repair_space>\\p{Lower}{4,5}" ) ; <END_BUG> Pattern goCommandNoParams = Pattern . compile ( "^go$" ) ; Pattern takeCmdWithoutParams = Pattern . compile ( "^take$" ) ; System . out . print ( "><seq2seq4repair_space>" ) ; command = in . readLine ( ) . trim ( ) ; Matcher goMatcher = goCommandFormat . matcher ( command ) ; Matcher goWithoutParams = goCommandNoParams . matcher ( command ) ; Matcher takeWithoutParams = takeCmdWithoutParams . matcher ( command ) ; if ( command . equals ( "help" ) ) { String response = gameService . manual ( ) ; System . out . println ( response ) ; } else if ( command . equals ( "?" ) ) { String response = gameService . intro ( ) ; System . out . println ( response ) ; } else if ( command . equals ( "look" ) ) { System . out . println ( player . look ( ) ) ; List < String > playersHere = gameService . listPlayersAt ( player . currentLocation ) ; if ( ( playersHere . size ( ) ) > 1 ) { playersHere . remove ( player . name ) ; System . out . println ( "Other<seq2seq4repair_space>players<seq2seq4repair_space>at<seq2seq4repair_space>this<seq2seq4repair_space>location:" ) ; for ( String playerName : playersHere ) { System . out . println ( ( "<seq2seq4repair_space>-<seq2seq4repair_space>" + playerName ) ) ; } } } else if ( command . equals ( "status" ) ) { System . out . println ( ( ( "You<seq2seq4repair_space>are<seq2seq4repair_space>" + ( player . name ) ) + "." ) ) ; if ( player . equipment . isEmpty ( ) ) { System . out . println ( "You<seq2seq4repair_space>have<seq2seq4repair_space>no<seq2seq4repair_space>items<seq2seq4repair_space>in<seq2seq4repair_space>the<seq2seq4repair_space>equipment." ) ; } else { System . out . println ( "Carrying:" ) ; for ( Item i : player . equipment ) { System . out . println ( i . name ) ; } } } else if ( goMatcher . matches ( ) ) { Direction direction = Direction . valueOf ( command . substring ( 3 ) . toUpperCase ( ) ) ; Location destination = gameService . from ( player . currentLocation , direction ) ; if ( destination != null ) { gameService . movePlayer ( player , destination ) ; player . currentLocation = destination ; } else { System . out . println ( "You<seq2seq4repair_space>can't<seq2seq4repair_space>go<seq2seq4repair_space>there." ) ; } } else if ( goWithoutParams . matches ( ) ) { System . out . println ( "Usage:\ngo<seq2seq4repair_space><direction>" ) ; System . out . println ( "<direction><seq2seq4repair_space>can<seq2seq4repair_space>be<seq2seq4repair_space>any<seq2seq4repair_space>of:" ) ; System . out . println ( "<seq2seq4repair_space>-<seq2seq4repair_space>north\n<seq2seq4repair_space>-<seq2seq4repair_space>east\n<seq2seq4repair_space>-<seq2seq4repair_space>south\n<seq2seq4repair_space>-<seq2seq4repair_space>west" ) ; } else if ( takeWithoutParams . matches ( ) ) { System . out . println ( "Usage:\ntake<seq2seq4repair_space><item>" ) ; } else if ( command . equals ( "where" ) ) { System . out . println ( ( "Your<seq2seq4repair_space>current<seq2seq4repair_space>location<seq2seq4repair_space>is<seq2seq4repair_space>" + ( player . currentLocation . name ) ) ) ; Map < Direction , Location > possibleDestinations = gameService . listAdjacentTo ( player . currentLocation ) ; if ( possibleDestinations != null ) { System . out . println ( "You<seq2seq4repair_space>can<seq2seq4repair_space>go:" ) ;

Fix:
Pattern goCommandFormat = Pattern . compile ( "^go<seq2seq4repair_space>(?:north|east|south|west)" ) ;